Shadowfiend / scala-2-13-scalap-primitive-parameter-detection

scalap 2.13.[0|1] issue with constructor parameters

This repo demonstrates an issue with scalap in Scala 2.13.0 and 2.13.1 whereby it does not report constructor parameters in the same way as Scala <2.12.

To show this, run the following two commands:

$ sbt "++2.12.9 run"
[info] Loading project definition from ...
[info] Loading settings for project scala-2-13-scalap-primitive-parameter-detection from build.sbt ...
[info] Set current project to scala-2-13-scalap-primitive-parameter-detection (in build ...)
[info] Setting Scala version to 2.12.9 on 1 projects.
[info] Reapplying settings...
[info] Set current project to scala-2-13-scalap-primitive-parameter-detection (in build ...)
[info] running code.Test
 - <init>: List(MethodSymbol(base, owner=2, flags=2000, info=15 ,None))
 - <init>: List(MethodSymbol(base, owner=2, flags=2000, info=15 ,None))
 - <init>: List(MethodSymbol(base, owner=2, flags=2000, info=15 ,None))
[success] Total time: 1 s, completed Sep 22, 2019, 10:06:52 PM
$ sbt "++2.13.1 run"
[info] Loading project definition from ...
[info] Loading settings for project scala-2-13-scalap-primitive-parameter-detection from build.sbt ...
[info] Set current project to scala-2-13-scalap-primitive-parameter-detection (in build ...)
[info] Setting Scala version to 2.13.1 on 1 projects.
[info] Reapplying settings...
[info] Set current project to scala-2-13-scalap-primitive-parameter-detection (in build ...)
[info] running code.Test
 - <init>: List()
 - <init>: List()
 - <init>: List()
[success] Total time: 1 s, completed Sep 22, 2019, 10:07:31 PM

In 2.12.9, the MethodSignature object for the constructor has one entry for children, the single constructor parameter. In 2.13.1, the object has no children at all, making it impossible to explore the constructor’s parameters.

Context

This was discovered while trying to make the tests for [lift-json](https://github.com/lift/framework/tree/master/core/json) run successfully for Scala 2.13.